Human blood neutrophils, similar to red cells, have antigenic polymorphism and have specific antigenic factors independent of HL-A and blood group systems. Neutrophil-specific antigens have been shown in vivo to be involved in the development of isoimmune neonatal neutropenia due to fetal-maternal incompatibility, autoimmune neutropenia, and febrile and pulmonary transfusion reactions. Furthermore, matching for these antigens may prove to be essential if febrile reactions to repeated leukocyte transfusion are to be avoided, and if leukocyte transplantation is to succeed. It is the purpose of this research to achieve the following: 1. A search for new specificities and procurement of new typing reagents. This will be achieved: a. by studying new cases of isoimmune neonatal neutropenia and obtaining maternal sera which contain antibody, and b. by preparation of xenogeneic anti-neutrophil antibodies, the immunizing agents being either whole neutrophils or purified antigens. 2. Improvement upon the existing techniques used for detection of antibodies, including microagglutination assay and the application of fluorescent microscopy for single cell typing. 3. Evaluation of biological importance of neutrophil-specific antigens, including relevance in bone marrow transplantation and neutropenias. 4. Solubilization and biochemical characterization of neutrophil antigens. Antigenic components will be extracted from neutrophils by standard membrane-solubilizing agents and further purified by polyacrylamide gel electrophoresis. The isolated antigens will be studied for chemical structure and screened for possible enzymatic activity. 5. Characterization of neutrophil antigens in primates. BIBLIOGRAPHIC REFERENCES: Jiang, A.F., and Lalezari, P.: A micro-technique for detection of leukocyte agglutinins. J. Immunological Methods 7:103, 1975. Lalezari, P., Jiang, A.F., Yegen, L., and Santorineou, M.: Chronic autoimmune neutropenia due to anti-NA2 antibody. N. Eng. J. Med. 293:744, 1975.